This invention relates generally to apparatus for weighing product and, more particularly, to a computerized scale for weighing product just prior to packaging of the product by an automatic packaging machine.
In general, a computerized scale of the foregoing type includes a series (e.g., ten) of so-called weighing buckets each associated with an underlying load cell or other means for producing an electrical signal representative of the weight of product in the bucket. Located above each weighing bucket is a holding bucket which contains a quantity of the product to be packaged. During each cycle, each empty weighing bucket is filled with product by momentarily opening the overlying holding bucket and allowing the product to fall into the weighing bucket. The weight of the product dropped into each weighing bucket is substantially less than the total weight of product which subsequently is placed in each package by the packaging machine.
After all of the weighing buckets have been filled, a computer responds to the weight signals produced by the different load cells, adds the weights in various combinations of weighing buckets and then selects the particular combination of buckets that meets the minimum statistical weight for the package to be filled while providing the least excess weight. The weighing buckets of that particular combination then are emptied and the product therein is delivered to the packaging machine to be deposited in the package.
Weighing buckets for conventional commercially available computer scales include doors which move to open positions to dump the product from the buckets after the product has been weighed. Because of the door and the need to open the weighing bucket, the rigidity of the bucket is reduced and its natural frequency is decreased. While high frequency disturbances in the bucket can be electronically filtered from the load cell signal in a relatively easy manner, low frequency disturbances resulting from a door-type bucket having a relatively low natural frequency are more difficult to eliminate and can result in inaccurate readings. In addition, the door of such a weighing bucket must close before the bucket can be re-filled and thus the time required for closing the door increases the time required for the overall weighing cycle.